Abstract: Based on the double cropping rice yield and soil nutrient situation in a sitespecific experiment during 2008 and 2013, we studied the effect of yearly milk vetch application on rice yield and its stability, and discussed the correlation between rice yield with soil nutrient variation. The results showed that milk vetch application significantly improved both early and late rice yields. Milk vetch application to early rice reduced the interannual variation of double cropping rice yield, and thus made the overall rice yield more stable. Increased soil fertility by milk vetch application was the decisive factor for increment of overall rice yield and yield stability. Further analysis showed that N released from milk vetch improved soil organic matter and total nitrogen more significantly than commensurate application of chemical fertilizer N. The application of milk vetch not only improved the productivity of paddy soil, but also made the productivity of paddy soil ecosystem more stable by raising its soil fertility. We conclude that using milk vetch as green manure can provide available nutrients in current season and improve soil fertility over a long period of time.

Key words: straw returning, N use efficiency, DCD, reducing N fertilizer